The invention relates to a system for indirectly monitoring the inflation pressure of a pneumatic-tyred vehicle wheel on vehicles, comprising at least one wheel body with a rim part and a disc part, comprising a tyre detachably fitted on the rim part of the wheel body, comprising a valve fitted in the wheel body and intended for changing the inflation pressure in the tyre, comprising at least one sensor for sensing the tyre inflation pressure at the time, comprising a data transmission device for transmitting sensor signals of the at least one sensor to an evaluation device, and comprising an evaluation device for evaluating the sensor signals, the at least one sensor being a deformation sensor. The invention also relates to a vehicle wheel for such a system comprising a wheel body, which has a disc part that can be fastened to a vehicle axle of a vehicle and a rim part for receiving a tyre, the wheel body being provided with a valve hole for fitting a valve for optionally changing an inflation pressure in the fitted tyre.
It has been known for years in the vehicle industry that the tyre pressure of a pneumatic-tyred vehicle wheel has a not inconsiderable influence on the safe operation of a vehicle. Not only does an incorrect tyre pressure lead to increased fuel consumption, and to this extent to inefficient operation of the vehicle, but also an inappropriate tyre pressure can cause considerable safety problems that can lead to accidents. In order to make it easier for the vehicle driver to monitor the tyre pressure, tyre pressure monitoring systems have therefore been designed for numerous vehicles, operating with the electronic system and signal indicating instruments of a vehicle to allow the tyre pressure to be indicated.
Most of the tyre pressure monitoring systems (TPMS) available on the market use for this purpose directly measuring pressure sensors that are assigned to the valve and transmit the tyre pressure value measured by the pressure sensor by way of an electronic system of the wheel equipped with a transmission antenna to a receiving device in the vehicle, which then in turn indicates the measured value by way of the electronic system of the vehicle and, if it is below a prescribed value, possibly triggers a warning signal. The directly measuring tyre pressure monitoring systems use relatively expensive and heavy sensors along with wheel electronics, which in each case leads to an imbalance in the vehicle wheel, which in turn has to be compensated by way of balancing weights. When a vehicle wheel is changed, there is an increased risk of damage to the inflation pressure sensor and/or the wheel electronics. Although directly measuring tyre pressure monitoring systems are most widely used, in spite of the weight of sometimes over 40 g for the measuring sensor along with the wheel electronics, they are overall technically disadvantageous for the operation of vehicles with vehicle wheels.
In the case of the directly measuring tyre pressure monitoring systems, leakage problems can occur, in particular in the case of high-speed vehicle wheels, for example on account of the centrifugal forces. Changed wheel geometries with minimal well depths or narrow well widths may also lead to problems in the fitting of valves equipped with directly measuring sensors. In the case of vehicle wheels that are to be equipped by the wheel manufacturer with directly measuring valves suitable for tyre pressure monitoring, the mounting and/or further processing of the vehicle wheels may lead to damage to the valves unless corresponding measures are taken to protect these valves, thereby increasing the handling effort involved.
In the case of military vehicles, it has been known for over 10 years to provide a rotary inflation pressure connection between the interior space in the tyre and a pressure controller in the vehicle, by way of which it is possible for the tyre pressure to be measured and changed while under way. These control systems are still more complex and expensive than the previously mentioned directly measuring tyre pressure monitoring systems, and therefore have not so far gained access to the market in the area of civilian passenger vehicles and in the area of heavy goods vehicles.
It is also known for example from DE 101 46 031 A1 to monitor the inflation pressure of a vehicle wheel by way of an indirect inflation pressure monitoring system. The previously known indirect inflation pressure monitoring systems rely on embedding a deformation sensor in the vehicle tyre and then using the measuring signals from the sensor for sensing and determining the tyre inflation pressure at the time. In the generically related DE 101 46 031 A1, a deformation sensor of the surface wave type is used, designed as a radio sensor and generating a signal corresponding to the respective deformation of the running surface, in particular in the circumferential direction, which is transmitted wirelessly to a signal receiver, which passes it on to an evaluation computer. The evaluation computer in turn uses characteristic maps previously recorded for a prescribed type of tyre, and stored in a map memory, for determining the inflation pressure of a tyre.